Enhanced ammonia oxidation on BDD induced by inhibition of oxygen evolution reaction

Electrochemical oxidation of ammonia (NH₃ and NH₄ ⁺ ) on boron-doped diamond (BDD) electrode was studied using differential electrochemical mass-spectrometry (DEMS) and chronoamperometry. Electro-oxidation of ammonia induces inhibition of the oxygen evolution reaction (OER) due to adsorption of the ammonia oxidation products on the BDD surface. The inhibition of the OER enhances ammonia electro-oxidation, which becomes the main reaction. The amino radicals, formed during ammonia oxidation, trigger a reaction chain in which molecular oxygen dissolved in solution is involved in the ammonia electro-oxidation. Nitrogen, nitrous oxide, and nitrogen dioxide were detected as the ammonia oxidation products, with nitrogen being the main gaseous product of the oxidation.     

Ammonia oxidation on electrodeposited Pt–Ir alloys

Ammonia electro-oxidation on Pt–Ir alloys has been studied applying cyclic voltammetry and differential electrochemical mass spectrometry (DEMS), and the results were compared with pure Pt. Bimetallic alloys were prepared by electrodeposition and characterized using X-ray diffractometry (XRD) and Auger spectroscopy, before and after oxidation of ammonia. Pt/Ir atomic composition was 70:30 obtained from 1:1 solutions. Substitution alloys were established where Ir atoms replace Pt positions in the face-centered cubic structure. Preferential crystal orientations were detected in the electrodeposits with the development of a crystallographic texture. DEMS showed that N₂ is the main product during ammonia oxidation for both Pt and Pt–Ir, but the formation of nitrogen oxides is observed for E > 0.8 V_RHE. The yield of N₂ is higher for the alloy, which also displays lower poisoning of the surface when increasing ammonia concentration. These results confirm Pt–Ir alloys as alternatives to Pt electrodes concerning ammonia oxidation. Finally, it was observed that XRD patterns, as well as texture coefficient values, change after using the electrodeposits for ammonia oxidation, with the less compact planes the more affected ones. Dedicated to Prof. Dr. Teresa Iwasita on the occasion of her 65th birthday in recognition of her numerous contributions to interfacial electrochemistry.     

The influence of Pt-activation on the corrosion of carbon in gas diffusion electrodes—A dems study

Investigations of the dependence on the potential of the anodic oxidation of carbon electrodes using differential electrochemical mass spectroscopy (DEMS) show that pure carbon is oxidized only at potentials higher than 0.9 V (RHE) (with CO₂ and, to a lesser extent, CO being the main products), and that Pt activation catalyzes the oxidation of a CO_surf surface layer to CO₂ at potentials between 0.6 and 0.8 mV (RHE), with the CO_surf being formed on the carbon at E>0.3 V (RHE).It is assumed that the Pt-induced carbon corrosion occurs in the neighbourhood of the Pt-sites, thus damaging the Pt to carbon contact. Surface segregation of Pt-clusters and a loss of catalytic activity is the result.     

Oxidative nucleophilic substitution of hydrogen in nitroarenes with phenylacetic acid derivatives

Oxidative nucleophilic substitution of hydrogen (ONSH) in nitroarenes with carbanion of isopropyl phenyl acetate gives various products depending on the conditions and oxidant. The reaction carried out in liquid ammonia and KMnO₄ oxidant gives iso-propyl α-hydroxy-α-nitroarylphenylacetates formed via hydroxylation of the initial ONSH products. In some cases additionally dimeric, trimeric and tetrameric products are formed. In THF and Bu₄N⁺MnO₄⁻ or DDQ oxidants simple ONSH products are formed whereas oxidation by dimethyl dioxirane (DMD) gave iso-propyl hydroxyaryl phenyl acetates. The dimeric and trimeric products are apparently formed via coupling of nitrobenzylic radicals generated in course of oxidation with nitrobenzylic carbanions of the ONSH products.     

Spectroscopic investigations of C3 primary alcohols on platinum electrodes in acid solutions.: Part I. n-propanol

The electrochemical behavior of n-propanol (n-PrOH) on polycrystalline Pt in acid solutions was investigated using in situ Fourier transform infrared spectroscopy (FTIRS) and on line differential electrochemical mass spectrometry (DEMS). The main products of n-PrOH oxidation are CO₂, propanal and propionic acid. Different types of adsorbates with one, two or three C atoms were detected. Ethane and propane are produced from n-PrOH adsorbates during potential cycling in the H-adatom potential region. An increase in the quantity of adsorbed CO was observed after hydrogenation of n-PrOH adsorbates.     

Catalytic Performance of Spherical MCM-41 Modified with Copper and Iron as Catalysts of NH3-SCR Process

Spherical MCM-41 with various copper and iron loadings was prepared by surfactant directed co-condensation method. The obtained samples were characterized with respect to their structure (X-ray diffraction, XRD), texture (N₂ sorption), morphology (scanning electron microscopy, SEM), chemical composition (inductively coupled plasma optical emission spectrometry, ICP-OES), surface acidity (temperature programmed desorption of ammonia, NH₃-TPD), form, and aggregation of iron and copper species (diffuse reflectance UV-Vis spectroscopy, UV-Vis DRS) as well as their reducibility (temperature programmed reduction with hydrogen, H₂-TPR). The spherical MCM-41 samples modified with transition metals were tested as catalysts of selective catalytic reduction of NO with ammonia (NH₃-SCR). Copper containing catalysts presented high catalytic activity at low-temperature NH₃-SCR with a very high selectivity to nitrogen, which is desired reaction products. Similar results were obtained for iron containing catalysts, however in this case the loadings and forms of iron incorporated into silica samples very strongly influenced catalytic performance of the studied samples. The efficiency of the NH₃-SCR process at higher temperatures was significantly limited by the side reaction of direct ammonia oxidation. The reactivity of ammonia molecules chemisorbed on the catalysts surface in NO reduction (NH₃-SCR) and their selective oxidation (NH₃-SCO) was verified by temperature-programmed surface reactions.     

A Spectroscopic Study on Nitrogen Electrooxidation to Nitrate

As a potential substitute technique for conventional nitrate production, electrocatalytic nitrogen oxidation reaction (NOR) is gaining more and more attention. But, the pathway of this reaction is still unknown owing to the lack of understanding on key reaction intermediates. Herein, electrochemical in situ attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) and isotope-labeled online differential electrochemical mass spectrometry (DEMS) are employed to study the NOR mechanism over a Rh catalyst. Based on the detected asymmetric NO₂⁻ bending, NO₃⁻ vibration, N=O stretching, and N−N stretching as well as isotope-labeled mass signals of N₂O and NO, it can be deduced that the NOR undergoes an associative mechanism (distal approach) and the strong N≡N bond in N₂ prefers to break concurrently with the hydroxyl addition in distal N.     

A Synthetic Method to Access Symmetric and Non-Symmetric 2-(<em>N</em>,<em>N</em><em>'</em>-disubstituted)guanidinebenzothiazoles

Symmetric and non-symmetric 2-(N-H, N-methyl, N-ethylenyl and N-aryl)guanidinebenzothiazoles were synthesized from the reaction of ammonia, methylamine, pyrrolidine and aniline with dimethyl benzo[d]thiazol-2-yl-carbono-dithioimidate (5) as intermediate. The products were characterized by ¹H-, ¹³C-NMR spectroscopy and three of them by X-ray diffraction analysis. HN-phenyl protons formed intramolecular hydrogen bonds that assist the stereochemistry of the second substituent, whereas the HN-alkyl protons were involved in intermolecular hydrogen bonding.     

Unveiling the Activity Origin of a Copper‐based Electrocatalyst for Selective Nitrate Reduction to Ammonia

Unveiling the active phase of catalytic materials under reaction conditions is important for the construction of efficient electrocatalysts for selective nitrate reduction to ammonia. The origin of the prominent activity enhancement for CuO (Faradaic efficiency: 95.8 %, Selectivity: 81.2 %) toward selective nitrate electroreduction to ammonia was probed. ¹⁵N isotope labeling experiments showed that ammonia originated from nitrate reduction. ¹H NMR spectroscopy and colorimetric methods were performed to quantify ammonia. In situ Raman and ex situ experiments revealed that CuO was electrochemically converted into Cu/Cu₂O, which serves as an active phase. The combined results of online differential electrochemical mass spectrometry (DEMS) and DFT calculations demonstrated that the electron transfer from Cu₂O to Cu at the interface could facilitate the formation of *NOH intermediate and suppress the hydrogen evolution reaction, leading to high selectivity and Faradaic efficiency.     

A Spectroscopic Study of Electrochemical Nitrogen and Nitrate Reduction on Rhodium Surfaces

Rh is a promising electrocatalyst for the nitrogen reduction reaction (NRR) given its suitable nitrogen‐adsorption energy and low overpotential. However, the NRR pathway on Rh surfaces remains unknown. In this study, we employ surface‐enhanced infrared‐absorption spectroscopy (SEIRAS) and differential electrochemical mass spectrometry (DEMS) to study the reaction mechanism of NRR on Rh. N₂H_x (0≤x≤2) is detected with a N=N stretching mode at ≈2020 cm^?1 by SEIRAS and a signal at m/z=29 by DEMS. A new two‐step reaction pathway on Rh surfaces is proposed that involves an electrochemical process with a two‐electron transfer to form N₂H₂ and its subsequent decomposition in the electrolyte producing NH₃. Our results also indicate that nitrate reduction and the NRR share the same reaction intermediate N₂H_x.     

Capacitance Polypyrrole‐based Impedimetric Immunosensor for Interleukin‐10 Cytokine Detection

In the present study, we developed a novel label‐free capacitance impedimetric immunosensor based on the immobilization of the human monoclonal antibody anti‐interleukin‐10 (anti‐IL‐10 mAb) onto polypyrrole (PPy)‐modified silicon nitride (Si₃N₄) substrates. The immunosensor was used for the detection of the recombinant interleukin‐10 antigen (rh IL‐10) that may be secreted in patients at the early stage of inflammation. The immunosensor was created by chemical deposition of PPy conducting layer on pyrrole?silane (SPy)‐treated Si/SiO₂/Si₃N₄ substrates (Si/SiO₂/Si₃N₄?SPy), followed by anti‐IL‐10 mAb immobilization through carboxyl‐functionalized diazonium (CMA) protocol and carbodiimide chemistry. The surface characterization and the biofunctionalization steps were characterized by SEM, FTIR and cyclic voltammetry (CV) while the detection process was carried out by using electrochemical impedance spectroscopy (EIS) analyses. The created immunosensor showed two linear fittings (R²=0.999) for the detection of rh IL‐10 within the concentration range from 1–50 pg/mL. It exhibited high sensitivity (0.1128 (pg/mL)^?1) with a very low limit of detection (LOD)=0.347 pg/mL, more particularly, at the low concentration range (1–10 pg/mL). Thus, this developed polypyrrole‐based immunosensor represents a promising strategy for creation of miniaturized label‐free, fast and highly sensitive biosensors for diagnosis of inflammation biomarkers at very low concentrations with reduced cost.     

Spectroscopic elucidation of reaction pathways of acetaldehyde on platinum and palladium in acidic media

The electrochemical behavior of acetaldehyde on palladium and platinum electrodes in acidic media was comparatively studied by means of differential electrochemical mass spectrometry (DEMS) and in situ Fourier transform infrared spectroscopy (FTIRS) combined with cyclic voltammetry. It was observed that acetaldehyde decomposition depends on the catalyst material, applied potential, and reactant concentration. Additionally, it was detected that acetaldehyde adsorbs and dissociates at potentials lower than 0.60 V vs RHE, producing methane and adsorbed CO on Pd; while C₂-species, CH_x and CO_ad are formed on Pt. Besides carbon dioxide, acetic acid and adsorbed acetate were observed at E?>?0.6 V, and their contribution increased with acetaldehyde concentration. Differences between Pt and Pd in potential dependence of the products and intermediates were established. Calibration of the mass spectrometer, together with the use of labeled acetaldehyde and IR spectra, allows establishment of the nature of adsorbed species and products for both Pt and Pd at different potentials, elucidating global reaction pathways for acetaldehyde on these two noble metals.     

Elementary steps of ethanol oxidation on Pt in sulfuric acid as evidenced by isotope labelling

The elementary steps of the anodic oxidation of ethanol on Pt in sulfuric acid are visualized with differential electrochemical mass spectroscopy (DEMS) by means of deuterium and ¹⁸O labelling. It turns out that: (i) ethanol is oxidized directly to acetaldehyde by the cleavage of one hydrogen of the α-C-atom and the hydroxyl hydrogen; (ii) a strongly bound intermediate is formed in parallel; (iii) the intermediate is oxidized at 0.7 V to give two CO₂ molecules, one originating from the alcoholic group and still containing the alcoholic O, the other from the methyl group; (iv) CC bond splitting seems to occur during the oxidation of the adsorbate only.     

Electrochemical impedance probing of DNA hybridisation on oligonucleotide-functionalised polypyrrole

We report a new approach for detecting DNA hybridisation using non faradaic electrochemical impedance spectroscopy. The technique was applied to a system of DNA probes bearing amine groups that are immobilized by covalent grafting on a supporting polypyrrole matrix functionalised with activated ester groups.The kinetics of the attachment of the ss-DNA probe was monitored using the temporal evolution of the open circuit potential (OCP). This measurement allows the determination of the time necessary for the chemical reaction of ss-DNA probe into the polypyrrole backbone.The hybridisation reactions with the DNA complementary target and non complementary target were investigated by non faradaic electrochemical impedance spectroscopy. Results show a significant modification in the Nyquist plot upon addition of the complementary target whereas, in presence of the non complementary target, the Nyquist plot is not modified. The spectra, in the form of Nyquist plot, were analysed with the Randles circuit. The transfer charge resistance R₂ shows a linear variation versus the complementary target concentration. Sensitivity and detection limit (0.2 nM) were determined and detection limit was lower of one order of magnitude than that obtained with the same system and measuring variation of the oxidation current at constant potential.     

Characterization of the polypyrrole film-piezoelectric sensor combination

Polymerization of pyrrole onto the electrode surfaces of thickness-shear-mode acoustic wave sensors at various levels of oxidation has been performed with electrochemical methods. The resulting films of polypyrrole have been characterized by scanning electron microscopy and X-ray photoelectron spectroscopy. Frequency decreases for the polypyrrole-coated sensors exposed to methanol, toluene and ammonia have been evaluated in terms of the various interactions occurring at the polymer surface.     

Reactivity of the radical cation of 4-(N,N-dialkylamino)biphenyl derivatives as probed by resonance Raman spectroscopy

The cw resonance Raman spectra of the products of electrochemical oxidation of 4-(N,N-dialkylamino)biphenyl compounds, with alkyl = methyl, methyl-d₃ or ethyl, are analyzed and compared with the time-resolved resonance Raman spectra of the photogenerated radical cation of these amines. The anodic oxidation is shown to lead to the formation of the respective N,N,N′,N′-tetraalkylbenzidine radical cation and dication, and a mechanism scheme for the oxidation is proposed.     

Electrochemical oxidation of molecular nitrogen to nitric acid – towards a molecular level understanding of the challenges

Nitric acid is manufactured by oxidizing ammonia where the ammonia comes from an energy demanding and non-eco-friendly, Haber–Bosch process. Electrochemical oxidation of N₂ to nitric acid using renewable electricity could be a promising alternative to bypass the ammonia route. In this work, we discuss the plausible reaction mechanisms of electrochemical N₂ oxidation (N₂OR) at the molecular level and its competition with the parasitic oxygen evolution reaction (OER). We suggest the design strategies for N₂ oxidation electro-catalysts by first comparing the performance of two catalysts – TiO₂(110) (poor OER catalyst) and IrO₂(110) (good OER catalyst), towards dinitrogen oxidation and then establish trends/scaling relations to correlate OER and N₂OR activities. The challenges associated with electrochemical N₂OR are highlighted.

Electrochemical oxidation of N₂ to HNO₃ (N₂OR) is explored in conjunction with parasitic oxygen evolution reaction (OER) on a poor and a good OER catalyst, TiO₂ and IrO₂. We develop scaling relations to correlate OER and N₂OR activities on oxides.     

Biosensors based on polymer networks formed by gamma irradiation crosslinking

Water-soluble polymers immobilized by gamma radiation have been investigated as a means of developing electrochemical sensors. Enzyme-based sensors for glucose and lactate have been made by immobilizing glucose oxidase and lactate oxidase, respectively, on platinized graphite electrodes. The enzyme is entrapped in a polymeric network of poly(vinyl alcohol) that is formed by gamma radiation crosslinking. Electrodes coated with poly (N-vinylpyrrolidone) and its corresponding monomer and then crosslinked with gamma radiation show an extraction of catecholamines into the polymer film that enhances the analytical signal for their detection by electrochemical oxidation. Poly(dimethyldiallylammonium chloride) spin-coated on a screen-printed electrochemical cell provides sufficient ionic conductivity for the cell to function as a gas sensor for oxygen, which is detected by reduction at a platinum working electrode.     

Modeling of ammonia oxidation on a platinoid catalyst,taking into account the N<Subscript>2</Subscript>O formation

A mathematical model of ammonia oxidation on a platinoid catalyst, taking into account the N₂O formation, was developed. The possibilities of lowering the amount of N₂O, which is formed as by-product in high-temperature oxidation of ammonia in nitric acid production, are examined. The developed model allows calculation of the reactor for ammonia oxidation using platinoid catalysts of different geometric profiles.     

Electrocatalytic oxidation of NADH on carbon black electrodes

Differential electrochemical mass spectroscopy (DEMS) was used to obtain information about the strongly adsorbed intermediate during methanol electrooxidation on platinum in sulfuric acid. It turned out that three electrons are released upon oxidation of one adsorbate molecule to CO₂. In the presence of oxygen, however, the number of electrons was determined to be between 2 and 2.5. Therefore CO can be excluded as the intermediate during methanol oxidation. COH seems to be the more likely adsorbate involved in the reaction pathway.